Stilbite

Stilbite is a tectosilicate mineral belonging to the zeolite group. It is a relatively common mineral found in basalt cavities, hydrothermal veins, and metamorphic rocks.

Etymology and History: The name Stilbite originates from the Greek word "stilbein," meaning "to glitter," referring to its pearly luster. It was first described in 1796 by Jean-Claude Delamétherie.

Chemical Composition and Structure: Stilbite's chemical formula is typically given as NaCa₂(Al₅Si₁₃)O₃₆·14H₂O. However, the sodium content can vary, and potassium may also be present. It features a framework structure consisting of linked aluminosilicate tetrahedra with channels and cavities that contain water molecules and exchangeable cations. The presence of water is crucial to its zeolite properties.

Physical Properties:

• Color: Commonly white, but can also be found in shades of yellow, brown, pink, or reddish.
• Luster: Pearly to vitreous.
• Crystal System: Monoclinic.
• Habit: Typically forms in sheaf-like or radiating aggregates of bladed crystals. Individual crystals are less common.
• Cleavage: Perfect on {010}.
• Fracture: Uneven.
• Hardness: 3.5 - 4 on the Mohs scale.
• Specific Gravity: 2.1 - 2.2.
• Streak: White.
• Transparency: Transparent to translucent.

Occurrence and Associations: Stilbite is frequently found in association with other zeolites such as apophyllite, heulandite, laumontite, and scolecite. It is commonly found in basalt cavities (vesicles) formed by gas bubbles in lava flows. Notable occurrences include India (especially the Deccan Traps), Iceland, Scotland, and the United States.

Uses: Stilbite, like other zeolites, has some industrial applications related to its ability to act as a molecular sieve. It can be used for adsorption, ion exchange, and catalysis. However, compared to other zeolites, stilbite's industrial uses are somewhat limited due to its lower stability and pore size. Its primary value is as a mineral specimen for collectors.

Distinguishing Characteristics: Stilbite can be identified by its characteristic sheaf-like habit, pearly luster, and perfect cleavage. Its relatively low hardness also helps to distinguish it from other minerals with similar appearance.